1. Field of the Invention
The present invention relates to an oxide superconducting film manufacturing apparatus, and more particularly, it relates to an oxide superconducting film manufacturing apparatus employing laser ablation method.
2. Description of the Background Art
When a target is irradiated with a laser beam, ablation so takes in a portion irradiated with the laser beam as to scatter particles of a material forming the target in states of atoms and molecules. The as-scattered particles are deposited on a substrate which is arranged to face the target, thereby providing a thin film of the material forming the target on the substrate.
When sputtering or MBE is employed for forming an oxide superconducting thin film, the interior of a thin film forming chamber must be maintained at a high degree of vacuum in general. When laser ablation method is employed, on the other hand, the interior of such a chamber may not be maintained at a high degree of vacuum but a film can be formed under a high gaseous oxygen pressure. Further, formation of a superconducting thin film by laser ablation method with an excimer laser, for example, is watched with interest in a point that a superconducting film of high quality can be formed at a high speed since scattered particles are deposited at a high speed and the composition of the as-formed film is hardly displaced from a target composition.
In formation of a superconducting film by such laser ablation method, an oxide superconducting film manufacturing apparatus shown in FIG. 5, for example, is employed in general. Referring to FIG. 5, this oxide superconducting film manufacturing apparatus comprises a laser oscillator 1, and a thin film forming chamber 3 having a laser entrance window 2. This laser oscillator 1 is set in the exterior of the thin film forming chamber 3. The thin film forming chamber 3 is provided therein with a target 4 containing components of an oxide superconductor, and a substrate 6 which is arranged to face the target 4.
The target 4 provided in the thin film forming chamber 3 is irradiated with a laser beam which is emitted from the laser oscillator 1, through the laser entrance window 2. The target 4 contains components of an oxide superconductor. Upon such irradiation with the laser beam, particles 5 of the material forming the target 4 are scattered from the target 4, to be deposited on the substrate 6 which is arranged to face the target 4. Thus, a thin film of the material forming the target 4 is provided on the substrate 6.
In such formation of a superconducting film by laser ablation method, however, the particles are scattered from the target 4 not only toward the substrate 6 but toward the laser entrance window 2 during film formation, to adhere to the laser entrance window 2. Thus, laser transmissivity of the laser entrance window 2 is so reduced that power of the laser beam which is applied to the target 4 is reduced with time. When the laser power is thus reduced with time, it is impossible to obtain a superconducting film having high characteristics.
Particularly in formation of a large area film such as a tape wire, a long time is required for film formation and hence the as-formed tape wire is irregularized in film quality and film thickness along its longitudinal direction due to the aforementioned reduction in laser power with time. Thus, it is impossible to obtain an oxide superconducting film having high and uniform characteristics.